1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, particularly, to a method of manufacturing a semiconductor device having a multi-layered wiring structure.
2. Description of the Related Art
In recent years, a buried Cu wiring in which a film having a low dielectric constant is used for forming an interlayer insulating film is widely used for improving the operating speed of semiconductor devices. A porous insulating film having fine pores is advantageous in that it makes it possible to secure a low relative dielectric constant of about 2.0. However, it is difficult for the porous insulating film noted above to obtain a sufficiently high wiring reliability.
To be more specific, an interlayer insulating film formed of a porous insulating film is likely to receive damage in forming a recess in the interlayer insulating film or in processing or removing a film deposited on the interlayer insulating film. As a result, generated are various problems such as an increase in the relative dielectric constant, a poor breakdown voltage between the adjacent wirings, peeling, cracking, and diffusion of the metal atoms. In order to avoid these problems, it is proposed to repair the damaged layer generated in the porous insulating film by treating with hexamethyl disilazane (HMDS) or dissolving the damaged layer by the treatment with, for example, a hydrogen fluoride for removing the damaged layer.
If the damaged layer is removed, the size of the recess such as a via or a wiring trench is increased, making it difficult to form the via or the wiring trench at a desired size. Also, where the damaged layer is repaired by the treatment with HMDS, it is certainly possible to restore the concentration of the carbon element in the damaged layer. However, it is impossible to obtain a sufficient increase in density. As a result, the metal is diffused into the porous film in a step of forming a metal wiring layer so as to give rise to the problem that the reliability of the wiring layer tends to be degraded. Thus, a new problem is generated as pointed out above even if the damaged layer is repaired or removed. A method of avoiding the influences given by the damaged layer generated in a porous insulating film without giving rise to any inconvenience has not yet been developed.
According to the technology node of “International Technology Roadmap of Semiconductor (ITRS)”, the minimum distance between the adjacent wirings after the 90 nm era will be less than about 0.1 μm and, thus, the metal diffused into the interlayer insulating film will cause a micro current leakage. As a result, the reliability of the metal wiring will be lowered. Since the distance between the adjacent wirings will be made further shorter in the era after the technology node of 65 nm, the problem derived from the diffusion of metal atoms will be made further prominent.